The use of radiofrequency (RF) generators and electrodes in neural tissue for the treatment of pain and functional disorders is well known. Included herein by reference, an as an example, the RFG-3C Plus RF Generator of Radionics, Inc., Burlington, Mass., and its associated electrodes are used in the treatment of the nervous system, and the treatment pain and functional disorders. This device is capable of delivering high frequency energy to patient tissue via an adapted electrode, and associated ground or reference electrode. This device is also capable of delivering low frequency stimulation pulses that are used to accurately localize the electrode placement before treatment. This unit delivers high frequency signal output both in a continuous RF mode and in a pulsatory RF mode, referred to as pulsed RF (PRF). In continuous RF mode, target tissue is heated near the uninsulated electrode tip of the high frequency electrode by the application of a high frequency signal output from the RF generator onto the tissue near the uninsulated electrode tip. For example, in continuous RF mode, it is common that a target tissue is heated in the range of 45 to 100° C. to selectively destroy the target tissue by heating. In the pulsed RF mode (PRF), intermittent bursts of high frequency signal output are delivered by the RF generator and applied to target tissue through the uninsulated electrode tip of the high frequency electrode. This is typically used to treat pain syndromes. The PRF signal output typically comprises a short period of on-time of high frequency signal, for example 0.1 to 50 milliseconds of on-time, followed by a period of off-time which has a duration that is substantially longer than the duration of the on-time (for example, 100 to 1000 milliseconds) in which the signal output is substantially lower than the signal output in the on-time burst, for example, near or at 0. The bursts of high frequency signal output are typically in the range of one to five bursts per second, referred to as pulses per second (pps), or Hertz (Hz). Because in PRF in the on-time period, signal output occurs for a short period, the amount of tissue heating near the uninsulated electrode tip of the high frequency electrode is reduced compared to, continuous RF mode for the same magnitude of signal output.
The RFG-3C Plus generator has one electrode output jack for connection to a single active electrode, and it has one reference electrode jack for connection to a reference electrode. When the active electrode is inserted into the body, and the reference electrode is placed, typically on the patient's skin, then RF current form the RF generate flows through the patient's body between the two electrodes. The generator can be activated and its signal output can be applied between the electrodes. Typically, this is referred to as a monopolar configuration because the active electrode is of smaller area than the reference electrode, and so the concentration of RF current is highest near it and the action of the RF electric field, whether for heating or for pulsed RF field therapy is greater there. This usually referred to as a single electrode configuration since there is only one “active” electrode.
Parameters that can be measured by the RFG-3C Plus RF generator include impedance, HF voltage, HF current, HF power, and electrode tip temperature. Parameters that may be set by the user include time of energy delivery, desired electrode temperature, stimulation frequencies and durations, and level of stimulation output. In general, electrode temperature is a parameter that may be controlled by the regulation of high frequency output power. Existing RF generators have interfaces that allow the selection of one or more of these treatment parameters, as well as various methods to display the parameters mentioned above.
In another example, the reference electrode can be inserted into the patient's body, and it can have an active area that is smaller and of comparable size to the active electrode. In that case, both electrodes become “active” in the sense that both of the have high temperature or electrical field effects on the tissues around them, so that they are both involved actively in the therapeutic effects the RF signal output. This can be referenced to as a single “bipolar” configuration.
A limitation for the monopolar and the bipolar configuration just described is that it limits the RF therapy to one or two electrode locations, respectively. In some situations it is desirable to treat more than one or two positions in the bodily tissue, and thus desirable to have more electrodes involved as the procedure goes on. For example, this can save time if there are multiple sites to be treated, as for example, multiple levels of the spinal medial branches to be treated for back pain.
The Untied Stated patent application Publication entitled Method and Apparatus for Diagnosing and Treating Neural Dysfunction, by W. J. Rittman, Pub. No. US 2007/0032835 A1, Pub. Date: Feb. 8, 2007, describes an RF generator system comprising an RF generator with multiple active electrode output connections that enables the RF signal output the generator to be connected and delivered simultaneously to more than one electrode to deliver a therapeutic effect at each of the electrode positions at the same time. The RF generator's signal output is switched by switches and switch controllers so that the RF generator's output is applied to multiple electrodes at the same time, that is, simultaneously. In another aspect, the RF generator's switches and switch controllers are independent, that is the switch and switch controller for one of the electrodes performs independently from those of a second electrode or from those of multiple individual electrodes. This has one disadvantage that, because the signal output can be applied to more than one electrode at the same time, the voltage of the generator's power supply and output electronics can be loaded down at the same time, causing sag or droop of the signal output voltage during application. Another disadvantage is that the electrical field from each of the electrodes adds coherently in the bodily tissue, making it more difficult to separate their individual effects on the bodily tissue. Another disadvantage is that it makes it more difficult to control the RF signal output and to maintain the RF signal output so as to maintain the temperatures of the electrodes at a set temperature chosen by the user.
Examples of high frequency generators and electrodes are given in the papers of entitled “Theoretical Aspects of Radiofrequency Lesions and the Dorsal Root Entry Zone,” by Cosman, E. R., et al., Neurosurgery 15:945-950, 1984; and “Methods of Making Nervous System Lesions,” by Cosman, E. R. and Cosman, B. J. in Wilkins R. H., Rengachary S. S. (eds): Neurosurgery, New York, McGraw-Hill, Vol. III, pp. 2490-2498, 1984, and are hereby incorporated by reference herein in their entirety.
Four patents have issued on PRF by Sluijter M. E., Rittman W. J., and Cosman E. R. They are “Method and Apparatus for Altering Neural Tissue Function,” U.S. Pat. No. 5,983,141, issued Nov. 9, 1999; “Method and System for Neural Tissue Modification,” U.S. Pat. No. 6,161,048, issued Dec. 12, 2000; “Modulated High Frequency Tissue Modification,” U.S. Pat. No. 6,246,912 B1, issued Jun. 12, 2001; and “Method and Apparatus for Altering Neural Tissue Function,” U.S. Pat. No. 6,259,952 B1, issued Jul. 10, 2001. These four patents are hereby incorporated by reference herein in their entirety.
In one example of the use of RF generators, a patient may complain of back pain, or some other pain of known or neuropathic origin. A clinician will often perform diagnostic blocks with local anesthetic by injecting the anesthetic into the areas that are suspected of generating the pain. If the patient receives temporary pain relief from these injections, the doctor concludes that the anatomical positions of the origin sites of the pain are in the locations where he made these injections. Unfortunately, the origin of pain is poorly understood; perceived pain at a certain level in the back, for instance, can actually be created from many different and multiple sources and anatomical locations.
Once a location has been identified, the clinician will decide to deliver high frequency signal output form a high frequency generator to this location to permanently destroy the source of the pain. A ground or reference plate will be placed on the patient's thigh to provide a return path for the high frequency energy. An insulated electrode with a small uninsulated tip will be placed at the expected target location. Stimulation pulses will be delivered at a sensory frequency (typically 50 Hz), and a stimulation voltage signal output will be applied to the electrode. The clinician is looking for a very low threshold of response from the patient (e.g., less than 0.5 V) to ensure that the electrode is close to the sensory nerves. They will then perform a stimulation test at a muscle motor frequency (e.g., 2 Hz), and increase the stimulation voltage output to 2 volts. In this instance, they are looking for no motor response in the patient's extremities as this would indicate the electrode was too close to the motor nerves. Treatment in this area could cause paralysis. Upon successful completion of these tests, high frequency energy is typically delivered for one or more minutes, while maintaining an electrode tip temperature between 70 and 90 degrees. Alternatively, high frequency signal output can be delivered for one or more minutes, but in a pulsed mode where the high frequency signal output is on for a short period of on-time and off for a long period of off-time, and thus the pulsed high frequency application will not produce any appreciable heating (reference is made to sited patents in the Background section herein)
Although these treatments are successful, they have several drawbacks. In practice, most patients need treatments at several different nerve locations. This requires placing the electrode, performing the stimulation, and delivering the high frequency signal output at each location, and then repeating the process. This can cause a great deal of wasted time, and patient discomfort, while waiting for the high frequency signal output to be delivered. Another drawback is that, in spite of successful stimulation testing; the target nerve is often not destroyed, thus resulting in no decrease of pain. The clinician is left to determine whether the target nerve has been missed, or whether the pain generator is located elsewhere in the body.